How do I change my Search Engine back to Google? It keeps using "installmac" instead.

Somehow I've probably gotten some sort of adware or malware or whatever, and I have this thing called installmac on my computer. Every time I go to search something up in my bar, it redirects to installmac something or another, and then goes through bing. Its obviously something messing with my computer and I really want it out. I don't know much about computers at all but I know thats not a good thing to have up there.